610 lines
21 KiB
HTML
610 lines
21 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>pthread_rwlockattr_getpshared()--Get Pshared Read/Write Lock
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Attribute</title>
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<!-- Begin Header Records ========================================== -->
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<!-- NETMG2 SCRIPT A converted by B2H R4.1 (346) (CMS) by HOLTJM at -->
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<!-- RCHVMW2 on 29 Jan 1999 at 10:01:37 -->
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<!--File Edited November 2001 --><!--End Header Records -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<!-- Java sync-link -->
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<script language="Javascript" src="../rzahg/synch.js" type="text/javascript">
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</script>
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<a name="Top_Of_Page"></a>
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<h2>pthread_rwlockattr_getpshared()--Get Pshared Read/Write Lock Attribute</h2>
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<div class="box" style="width: 70%;">
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<br>
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Syntax:
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<pre>
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#include <pthread.h>
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int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t *attr,
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int *pshared);
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</pre>
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<br>
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Service Program Name: QP0WPTHR<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE <br>
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<!-- iddvc RMBR -->
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<br>
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Threadsafe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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Signal Safe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<p>The <strong>pthread_rwlockattr_getpshared</strong>() function retrieves the
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current setting of the process shared attribute from the read/write lock
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attributes object. The process shared attribute indicates whether the
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read/write lock that is created using the read/write lock attributes object can
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be shared between threads in separate processes
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(<strong>PTHREAD_PROCESS_SHARED</strong>) or shared only between threads within
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the same process (<strong>PTHREAD_PROCESS_PRIVATE</strong>).</p>
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<p>Even if the read/write lock in storage is accessible from two separate
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processes, it cannot be used from both processes unless the process shared
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attribute is <strong>PTHREAD_PROCESS_SHARED</strong>.</p>
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<p>The default pshared attribute for read/write lock attributes objects is
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<strong>PTHREAD_PROCESS_PRIVATE</strong>.</p>
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<br>
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<h3>Authorities and Locks</h3>
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<p>None.</p>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong>attr</strong></dt>
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<dd>(Input) Address of the variable that contains the read/write lock
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attributes object</dd>
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<dt><strong>pshared</strong></dt>
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<dd>(Output) Address of the variable to contain the pshared attribute
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result</dd>
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</dl>
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<br>
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<h3>Return Value</h3>
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<dl>
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<dt><strong>0</strong></dt>
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<dd><strong>pthread_rwlockattr_getpshared</strong>() was successful.</dd>
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<dt><strong>value</strong></dt>
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<dd><strong>pthread_rwlockattr_getpshared</strong>() was not successful. <em>
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value</em> is set to indicate the error condition.</dd>
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</dl>
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<br>
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<h3>Error Conditions</h3>
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<p>If <strong>pthread_rwlockattr_getpshared</strong>() was not successful, the
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error condition returned usually indicates one of the following errors. Under
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some conditions, the value returned could indicate an error other than those
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listed here.</p>
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<dl>
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<dt><em>[EINVAL]</em></dt>
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<dd><p>The value specified for the argument is not correct.</p></dd>
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</dl>
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<br>
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<h3>Related Information</h3>
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<ul>
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<li>The <<strong>pthread.h</strong>> header file. See <a href=
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"rzah4hed.htm">Header files for Pthread functions</a>.<br><br></li>
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<li><a href="users_83.htm">pthread_rwlockattr_init()</a>--Initialize Read/Write
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Lock Attribute<br><br></li>
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<li><a href="users_84.htm">pthread_rwlockattr_setpshared()</a>--Set Pshared
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Read/Write Lock Attribute<br><br></li>
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<li><a href="users_86.htm">pthread_rwlock_init()</a>--Initialize Read/Write
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Lock</li>
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</ul>
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<br>
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<h3><a name="371750">Example</a></h3>
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<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
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for information pertaining to code examples.</p>
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<pre>
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#define _MULTI_THREADED
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#include <pthread.h>
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#include <stdio.h>
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#include <spawn.h>
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#include <sys/wait.h>
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#include <unistd.h>
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#include <sys/shm.h>
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#include "check.h"
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typedef struct {
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int protectedResource;
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pthread_rwlock_t rwlock;
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} shared_data_t;
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extern char **environ;
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shared_data_t *sharedMem=NULL;
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pid_t childPid=0;
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int childStatus=-99;
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int shmid=0;
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/* Change this path to be the path to where you create this example program */
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#define MYPATH "/QSYS.LIB/QP0WTEST.LIB/TPRWLSH0.PGM"
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#define NTHREADSTHISJOB 2
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#define NTHREADSTOTAL 4
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void parentSetup(void);
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void childSetup(void);
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void parentCleanup(void);
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void childCleanup(void);
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void *childReaderThreadFunc(void *parm)
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{
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int rc;
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int retries = 5;
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while (retries--) {
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rc = pthread_rwlock_rdlock(&sharedMem->rwlock);
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checkResults("pthread_rwlock_rdlock()\n", rc);
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/* Under protection of the shared read lock, read the resource */
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printf("CHILD READER - current protectedResource = %d\n",
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sharedMem->protectedResource);
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sleep(1);
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printf("CHILD READER - unlock\n");
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rc = pthread_rwlock_unlock(&sharedMem->rwlock);
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checkResults("pthread_rwlock_unlock()\n", rc);
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}
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return NULL;
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}
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void *parentWriterThreadFunc(void *parm)
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{
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int rc;
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rc = pthread_rwlock_wrlock(&sharedMem->rwlock);
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checkResults("pthread_rwlock_rdlock()\n", rc);
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/* Under protection of the exclusive write lock, write the resource */
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++sharedMem->protectedResource;
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printf("PARENT WRITER - current protectedResource = %d\n",
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sharedMem->protectedResource);
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sleep(5);
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printf("PARENT WRITER - unlock\n");
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rc = pthread_rwlock_unlock(&sharedMem->rwlock);
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checkResults("pthread_rwlock_unlock()\n", rc);
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return NULL;
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}
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int main(int argc, char **argv)
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{
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int rc=0;
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int i;
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pthread_t threadid[NTHREADSTHISJOB];
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int parentJob=0;
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void *status=NULL;
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/* If we run this from the QSHELL interpreter on the system, we want */
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/* it to be line buffered even if we run it in batch so the output between*/
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/* parent and child is intermixed. */
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setvbuf(stdout,NULL,_IOLBF,4096);
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/* Determine if we are running in the parent or child */
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if (argc != 1 && argc != 2) {
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printf("Incorrect usage\n");
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printf("Pass no parameters to run as the parent testcase\n");
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printf("Pass one parameter `ASCHILD' to run as the child testcase\n");
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exit(1);
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}
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if (argc == 1) {
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parentJob = 1;
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}
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else {
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if (strcmp(argv[1], "ASCHILD")) {
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printf("Incorrect usage\n");
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printf("Pass no parameters to run as the parent testcase\n");
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printf("Pass one parameter `ASCHILD' to run as the child testcase\n");
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exit(1);
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}
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parentJob = 0;
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}
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/* PARENT *****************************************************************/
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if (parentJob) {
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printf("PARENT - Enter Testcase - %s\n", argv[0]);
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parentSetup();
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printf("PARENT - Create %d threads\n", NTHREADSTHISJOB);
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for (i=0; i<NTHREADSTHISJOB; ++i) {
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rc = pthread_create(&threadid[i], NULL, parentWriterThreadFunc, NULL);
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checkResults("pthread_create()\n", rc);
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}
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for (i=0; i<NTHREADSTHISJOB; ++i) {
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rc = pthread_join(threadid[i], NULL);
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checkResults("pthread_create()\n", rc);
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if (status != NULL) {
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printf("PARENT - Got a bad status from a thread, "
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"%.8x %.8x %.8x %.8x\n", status);
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exit(1);
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}
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}
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parentCleanup();
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printf("PARENT - Main completed\n");
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exit(0);
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}
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/* CHILD *****************************************************************/
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{
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printf("CHILD - Enter Testcase - %s\n", argv[0]);
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childSetup();
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printf("CHILD - Create %d threads\n", NTHREADSTHISJOB);
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for (i=0; i<NTHREADSTHISJOB; ++i) {
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rc = pthread_create(&threadid[i], NULL, childReaderThreadFunc, NULL);
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checkResults("pthread_create()\n", rc);
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}
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/* The parent will wake up all of these threads using the */
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/* pshared condition variable. We will just join to them... */
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printf("CHILD - Joining to all threads\n");
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for (i=0; i<NTHREADSTHISJOB; ++i) {
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rc = pthread_join(threadid[i], &status);
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checkResults("pthread_join()\n", rc);
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if (status != NULL) {
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printf("CHILD - Got a bad status from a thread, "
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"%.8x %.8x %.8x %.8x\n", status);
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exit(1);
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}
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}
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/* After all the threads are awake, the parent will destroy */
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/* the read/write lock. Do not use it anymore */
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childCleanup();
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printf("CHILD - Main completed\n");
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}
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return 0;
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}
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/***************************************************************/
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/* This function initializes the shared memory for the job, */
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/* sets up the environment variable indicating where the shared*/
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/* memory is, and spawns the child job. */
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/* */
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/* It creates and initializes the shared memory segment, and */
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/* It initializes the following global variables in this */
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/* job. */
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/* sharedMem */
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/* childPid */
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/* shmid */
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/* */
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/* If any of this setup/initialization fails, it will exit(1) */
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/* and terminate the test. */
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/* */
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/***************************************************************/
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void parentSetup(void)
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{
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int rc;
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/***************************************************************/
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/* Create shared memory for shared_data_t above */
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/* attach the shared memory */
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/* set the static/global sharedMem pointer to it */
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/***************************************************************/
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printf("PARENT - Create the shared memory segment\n");
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rc = shmget(IPC_PRIVATE, sizeof(shared_data_t), 0666);
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if (rc == -1) {
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printf("PARENT - Failed to create a shared memory segment\n");
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exit(1);
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}
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shmid = rc;
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printf("PARENT - Attach the shared memory\n");
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sharedMem = shmat(shmid, NULL, 0);
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if (sharedMem == NULL) {
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shmctl(shmid, IPC_RMID, NULL);
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printf("PARENT - Failed to attach shared memory\n");
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exit(1);
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}
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/***************************************************************/
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/* Initialize the read/write lock and other shared memory data */
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/***************************************************************/
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{
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pthread_rwlockattr_t rwlattr;
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printf("PARENT - Init shared memory and read/write lock\n");
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memset(sharedMem, 0, sizeof(shared_data_t));
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/* Process Shared Read/Write lock */
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rc = pthread_rwlockattr_init(&rwlattr);
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checkResults("pthread_rwlockattr_init()\n", rc);
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rc = pthread_rwlockattr_setpshared(&rwlattr, PTHREAD_PROCESS_SHARED);
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checkResults("pthread_rwlockattr_setpshared()\n", rc);
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rc = pthread_rwlock_init(&sharedMem->rwlock, &rwlattr);
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checkResults("pthread_rwlock_init()\n", rc);
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}
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/**************************************************************/
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/* Set and environment variable so that the child can inherit */
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/* it and know the shared memory ID */
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/**************************************************************/
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{
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char shmIdEnvVar[128];
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sprintf(shmIdEnvVar, "TPRWLSH0_SHMID=%d\n", shmid);
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rc = putenv(shmIdEnvVar);
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if (rc) {
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printf("PARENT - Failed to store env var %s, errno=%d\n",
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shmIdEnvVar, errno);
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exit(1);
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|
}
|
||
|
|
printf("PARENT - Stored shared memory id of %d\n", shmid);
|
||
|
|
}
|
||
|
|
|
||
|
|
/**************************************************/
|
||
|
|
/* Spawn the child job */
|
||
|
|
/**************************************************/
|
||
|
|
{
|
||
|
|
inheritance_t in;
|
||
|
|
char *av[3] = {NULL, NULL, NULL};
|
||
|
|
|
||
|
|
/* Allow thread creation in the spawned child */
|
||
|
|
memset(&in, 0, sizeof(in));
|
||
|
|
in.flags = SPAWN_SETTHREAD_NP;
|
||
|
|
|
||
|
|
/* Set up the arguments to pass to spawn based on the */
|
||
|
|
/* arguments passed in */
|
||
|
|
av[0] = MYPATH;
|
||
|
|
av[1] = "ASCHILD";
|
||
|
|
av[2] = NULL;
|
||
|
|
|
||
|
|
/* Spawn the child that was specified, inheriting all */
|
||
|
|
/* of the environment variables. */
|
||
|
|
childPid = spawn(MYPATH, 0, NULL, &in, av, environ);
|
||
|
|
if (childPid == -1) {
|
||
|
|
/* spawn failure */
|
||
|
|
printf("PARENT - spawn() failed, errno=%d\n", errno);
|
||
|
|
exit(1);
|
||
|
|
}
|
||
|
|
|
||
|
|
printf("PARENT - spawn() success, [PID=%d]\n", childPid);
|
||
|
|
}
|
||
|
|
|
||
|
|
return;
|
||
|
|
}
|
||
|
|
|
||
|
|
/***************************************************************/
|
||
|
|
/* This function attaches the shared memory for the child job, */
|
||
|
|
/* It uses the environment variable indicating where the shared*/
|
||
|
|
/* memory is. */
|
||
|
|
/* */
|
||
|
|
/* If any of this setup/initialization fails, it will exit(1) */
|
||
|
|
/* and terminate the test. */
|
||
|
|
/* */
|
||
|
|
/* It initializes the following global variables: */
|
||
|
|
/* sharedMem */
|
||
|
|
/* shmid */
|
||
|
|
/***************************************************************/
|
||
|
|
void childSetup(void)
|
||
|
|
{
|
||
|
|
int rc;
|
||
|
|
|
||
|
|
printf("CHILD - Child setup\n");
|
||
|
|
/**************************************************************/
|
||
|
|
/* Set and environment variable so that the child can inherit */
|
||
|
|
/* it and know the shared memory ID */
|
||
|
|
/**************************************************************/
|
||
|
|
{
|
||
|
|
char *shmIdEnvVar;
|
||
|
|
shmIdEnvVar = getenv("TPRWLSH0_SHMID");
|
||
|
|
if (shmIdEnvVar == NULL) {
|
||
|
|
printf("CHILD - Failed to get env var \"TPRWLSH0_SHMID\", errno=%d\n",
|
||
|
|
errno);
|
||
|
|
exit(1);
|
||
|
|
}
|
||
|
|
shmid = atoi(shmIdEnvVar);
|
||
|
|
printf("CHILD - Got shared memory id of %d\n", shmid);
|
||
|
|
}
|
||
|
|
/***************************************************************/
|
||
|
|
/* Create shared memory for shared_data_t above */
|
||
|
|
/* attach the shared memory */
|
||
|
|
/* set the static/global sharedMem pointer to it */
|
||
|
|
/***************************************************************/
|
||
|
|
printf("CHILD - Attach the shared memory\n");
|
||
|
|
sharedMem = shmat(shmid, NULL, 0);
|
||
|
|
if (sharedMem == NULL) {
|
||
|
|
shmctl(shmid, IPC_RMID, NULL);
|
||
|
|
printf("CHILD - Failed to attach shared memory\n");
|
||
|
|
exit(1);
|
||
|
|
}
|
||
|
|
return;
|
||
|
|
}
|
||
|
|
|
||
|
|
/***************************************************************/
|
||
|
|
/* wait for child to complete and get return code. */
|
||
|
|
/* Destroy read/write lock in shared memory */
|
||
|
|
/* detach and remove shared memory */
|
||
|
|
/* set the child's return code in global storage */
|
||
|
|
/* */
|
||
|
|
/* If this function fails, it will call exit(1) */
|
||
|
|
/* */
|
||
|
|
/* This function sets the following global variables: */
|
||
|
|
/* sharedMem */
|
||
|
|
/* childStatus */
|
||
|
|
/* shmid */
|
||
|
|
/***************************************************************/
|
||
|
|
void parentCleanup(void)
|
||
|
|
{
|
||
|
|
int status=0;
|
||
|
|
int rc;
|
||
|
|
int waitedPid=0;
|
||
|
|
|
||
|
|
/* Even though there is no thread left in the child using the */
|
||
|
|
/* contents of the shared memory, before we destroy the */
|
||
|
|
/* read/write lock in that shared memory, we will wait for the */
|
||
|
|
/* child job to complete, we know for 100% certainty that no */
|
||
|
|
/* threads in the child are using it then, because the child */
|
||
|
|
/* is terminated. */
|
||
|
|
printf("PARENT - Parent cleanup\n");
|
||
|
|
/* Wait for the child to complete */
|
||
|
|
waitedPid = waitpid(childPid,&status,0);
|
||
|
|
if (rc == -1) {
|
||
|
|
printf("PARENT - waitpid failed, errno=%d\n", errno);
|
||
|
|
exit(1);
|
||
|
|
}
|
||
|
|
childStatus = status;
|
||
|
|
|
||
|
|
/* Cleanup resources */
|
||
|
|
rc = pthread_rwlock_destroy(&sharedMem->rwlock);
|
||
|
|
checkResults("pthread_rwlock_destroy()\n", rc);
|
||
|
|
|
||
|
|
/* Detach/Remove shared memory */
|
||
|
|
rc = shmdt(sharedMem);
|
||
|
|
if (rc) {
|
||
|
|
printf("PARENT - Failed to detach shared memory, errno=%d\n", errno);
|
||
|
|
exit(1);
|
||
|
|
}
|
||
|
|
rc = shmctl(shmid, IPC_RMID, NULL);
|
||
|
|
if (rc) {
|
||
|
|
printf("PARENT - Failed to remove shared memory id=%d, errno=%d\n",
|
||
|
|
shmid, errno);
|
||
|
|
exit(1);
|
||
|
|
}
|
||
|
|
shmid = 0;
|
||
|
|
return;
|
||
|
|
}
|
||
|
|
|
||
|
|
/***************************************************************/
|
||
|
|
/* Detach the shared memory */
|
||
|
|
/* At this point, there is no serialization, so the contents */
|
||
|
|
/* of the shared memory should not be used. */
|
||
|
|
/* */
|
||
|
|
/* If this function fails, it will call exit(1) */
|
||
|
|
/* */
|
||
|
|
/* This function sets the following global variables: */
|
||
|
|
/* sharedMem */
|
||
|
|
/***************************************************************/
|
||
|
|
void childCleanup(void)
|
||
|
|
{
|
||
|
|
int rc;
|
||
|
|
|
||
|
|
printf("CHILD - Child cleanup\n");
|
||
|
|
rc = shmdt(sharedMem);
|
||
|
|
sharedMem = NULL;
|
||
|
|
if (rc) {
|
||
|
|
printf("CHILD - Failed to detach shared memory, errno=%d\n", errno);
|
||
|
|
exit(1);
|
||
|
|
}
|
||
|
|
return;
|
||
|
|
}
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
<p><strong>Output:</strong></p>
|
||
|
|
|
||
|
|
<p>This example was run under the i5/OS QShell Interpreter. In the QShell
|
||
|
|
Interpreter, a program gets descriptors 0, 1, 2 as the standard files, the
|
||
|
|
parent and child I/O is directed to the console. When run in the QShell
|
||
|
|
Interpreter, the output shows the intermixed output from both parent and child
|
||
|
|
processes, and gives a feeling for the time sequence of operations occurring in
|
||
|
|
each job.</p>
|
||
|
|
|
||
|
|
<p>The QShell interpreter allows you to run multithreaded programs as if they
|
||
|
|
were interactive. See the QShell documentation for a description of the
|
||
|
|
QIBM_MULTI_THREADED shell variable which allows you to start multithreaded
|
||
|
|
programs.</p>
|
||
|
|
|
||
|
|
<p>The QShell Interpreter is option 30 of Base i5/OS.</p>
|
||
|
|
|
||
|
|
<pre>
|
||
|
|
PARENT - Enter Testcase - QP0WTEST/TPRWLSH0
|
||
|
|
PARENT - Create the shared memory segment
|
||
|
|
PARENT - Attach the shared memory
|
||
|
|
PARENT - Init shared memory and read/write lock
|
||
|
|
PARENT - Stored shared memory id of 7
|
||
|
|
PARENT - spawn() success, [PID=584]
|
||
|
|
PARENT - Create 2 threads
|
||
|
|
PARENT WRITER - current protectedResource = 1
|
||
|
|
CHILD - Enter Testcase - QP0WTEST/TPRWLSH0
|
||
|
|
CHILD - Child setup
|
||
|
|
CHILD - Got shared memory id of 7
|
||
|
|
CHILD - Attach the shared memory
|
||
|
|
CHILD - Create 2 threads
|
||
|
|
CHILD - Joining to all threads
|
||
|
|
PARENT WRITER - unlock
|
||
|
|
PARENT WRITER - current protectedResource = 2
|
||
|
|
PARENT WRITER - unlock
|
||
|
|
CHILD READER - current protectedResource = 2
|
||
|
|
CHILD READER - current protectedResource = 2
|
||
|
|
PARENT - Parent cleanup
|
||
|
|
CHILD READER - unlock
|
||
|
|
CHILD READER - current protectedResource = 2
|
||
|
|
CHILD READER - unlock
|
||
|
|
CHILD READER - current protectedResource = 2
|
||
|
|
CHILD READER - unlock
|
||
|
|
CHILD READER - current protectedResource = 2
|
||
|
|
CHILD READER - unlock
|
||
|
|
CHILD READER - current protectedResource = 2
|
||
|
|
CHILD READER - unlock
|
||
|
|
CHILD READER - current protectedResource = 2
|
||
|
|
CHILD READER - unlock
|
||
|
|
CHILD READER - current protectedResource = 2
|
||
|
|
CHILD READER - unlock
|
||
|
|
CHILD READER - current protectedResource = 2
|
||
|
|
CHILD READER - unlock
|
||
|
|
CHILD READER - current protectedResource = 2
|
||
|
|
CHILD READER - unlock
|
||
|
|
CHILD READER - unlock
|
||
|
|
CHILD - Child cleanup
|
||
|
|
CHILD - Main completed
|
||
|
|
PARENT - Main completed
|
||
|
|
</pre>
|
||
|
|
<br>
|
||
|
|
<hr>
|
||
|
|
API introduced: V4R3
|
||
|
|
<hr>
|
||
|
|
<center>
|
||
|
|
<table cellpadding="2" cellspacing="2">
|
||
|
|
<tr align="center">
|
||
|
|
<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
|
||
|
|
"rzah4mst.htm">Pthread APIs</a> | <a href="aplist.htm">APIs by
|
||
|
|
category</a></td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
</center>
|
||
|
|
</body>
|
||
|
|
</html>
|
||
|
|
|